/Engine/Source/Runtime/UMG/Public/Components/PanelWidget.h
Adds a new child widget to the container. Returns the base slot type, requires casting to turn it into the type specific to the container.
[UPanelSlot](API\Runtime\UMG\Components\UPanelSlot) * AddChild ( [UWidget](API\Runtime\UMG\Components\UWidget) * Content )